There are many good shrub roses that can attain considerable proportions with little attention other than a couple of cups of Rose Tone in the spring. Here are a few of my favorites: 'Applejack' gets to be about 6' x 6' in zone 4 and will be bigger in zone 6. It has rather informal light pink flowers that come in several flushes throughout the summer. This is a tough rose but does need full sun. 'Alba Semi-Plena' makes a huge shrub to 8' tall with beautiful fragrant flowers in the spring. It is very tough and can take some shade for part of the day. 'Celsiana' is a Damask that can get over 6' in my zone 4 garden. It has beautiful informal light pink flowers. 'Cerise Bouquet' is a huge rose that has reached about 10' x 10' for me. It flowers once in the spring. 'Clair Matin' is an outstanding modern shrub rose that gets to be about 6' x 6' for me in zone 6. 'Complicata' is a wonderful old gallica that easily makes 6' x 6'. It is hardy and reliable with little attention and has huge single pink flowers. 'Constance Spry' is one of the original Austin roses and still one of his best. The flowers a huge and very cupped. The plant is lax and needs some careful pruning to look its best. Fortunately, it suckers so will make a nice thicket over time. I keep mine about 5'. 'Eddie's Jewel' is one of the Moyesii hybrids and has deep red flowers on a 8' x 6' shrub. All the Moyesii hybrids make huge beautiful shrubs that flower once and require little care. 'Green Mantle' is my favorite of the Eglantine hydrids. As they are all quite similar any will do in this situation. They make 8' x 6' shrubs and are hardy and reliable. The frangrance of the foliage after a rain can be enjoyed 100 meters away. 'Harison's Yellow', the yellow rose of Texas, was found in a garden off Broadway in NY city about 1830. It has made its way all across the country. It makes a nice shrub about 6' x 5' for me in zone 6. It is about the first rose to bloom. It looks great with 'Cardinal de Richelieu' in front of it. 'Ispahan' is a Centifolia that makes a very tall but lax shrub. It is hardy even to zone 4. 'James Mason' is an outstanding modern srub rose with gallica genes. This rose easily makes 8' and does sucker around making an outstanding thicket of canes. It is very tough in zone 6 and grows with little care in partial shade. 'Lavender Lassie' is a modern shrub that gets to be about 6' x 6'. It blooms regularly throughout the summer with OGR type blooms. It is another of the outstanding roses from Kordes. 'Mme. Plantier' is a hybrid China rose from 1835. Everyone should have this rose. It makes a lax shrub 6' x 6' and blooms once with small very double white flowers. It is tough and reliable. 'Pleine de Grace' Now this is a shrub rose! My 14 year old plant knows no bounds. Its self supporting canes can easily reach 12' and with support will make another 6'. The flowers are profuse, white, single and about the size of a quarter. 'R. hugonis' is one of my favorite roses and makes a nice shrub easily 6' by 8'. It is one of the first to bloom with clear yellow flowers. Its fine foliage is rarely eaten by Japanese beetles. 'R. moyesii 'Highdownensis' is another of the Moyesii hybrids. I have to include it as it is such an outstanding rose. It will easily make a self supporting 10' shrub in zone 4. It is really a small tree and when in flower will have hundreds of flowers that makes for a spectacular landscape specimen visible for 100 meters. 'Roseraie de l' Hay' is a rugosa hybrid that makes a compact shrub about 6' x 5' with lush foliage that is disease free. It flowers several times throughout the summer and makes and outstanding and reliable shrub. 'Sara Van Fleet' is another rugosa hybrid. It gets to be about 6' x 5' for me in zone 4. It has light pink flowers and does suffer some dieback of unripe wood . 'Scharlachglut' is another modern shrub rose from Kordes. Its canes form a nice vase shaped shrub to 6' x 6' and is very hardy reliable and tough. The flowers are red and single. The hips are outstanding and pear shaped coming in huge bunches. Well, that should get you started. All of the above roses are easy to grow and require basic care of pruning out old wood and a spring application of fertilizer. I grow them with other shrubs and perennials in a mixed border for a nice display spring, summer and fall.

Lavender, marjoram, oregano, rosemary, sage, santolina, bay, basil, savory and thyme are the best known. Like Fatamorgana, I also do not like sand in soil mixes - if nothing else, they make the pot too heavy to lift! A good-quality, general-purpose potting mix is, IMO, the best option. Potted plants, which are always high maintenance, will need a little all-purpose fertiliser added from time to time - say once a year or so (add a handful of compost, or sprinkle on some slow-release pellets), and a potted plant will need more frequent watering. A thorough soaking once a week is better than a brief sip daily. But don't rely on the clock or calender for watering - use the finger-test and judge for yourself when a plant needs watering. Most of the Mediterrean plants can take quite a lot of water - as long as it drains away quickly. They don't like wet feet, but in a pot the soil is best kept barely moist. When planted in the garden, Mediterrean herbs generally can be left to their own devices - but they are definitely NOT desert plants, so in dry or very hot weather, give them a drink. Basil needs more water and fertiliser than most of its compatriots. Remember, too, to treat baby plants with a little more TLC than you'd treat mature adult plants. Mostly this means protecting them from the harshest conditions (too hot, too cold, too dry, too wet, too windy, too much fertiliser etc). Most of the Mediterrean plants like full sun (as much as they can get), and plenty of heat to make their leaves produce more of the essential oils which give them their flavour and aroma. The site below provides information about the 'Mediterranean climate'. Here is a link that might be useful: Mediterranean climate

It would still help to know where you are gardening if you would like more pertinent climate specific plant recommendations. Unless you are up in the Sierra Nevada foothills at sufficient elevation to receive significant snowfall, it is also highly unlikely you are receiving 6 feet of rain in an average year. Kentfield in Marin County is one of the local wettest spots in the SF Bay Area, and even they don't get this much rain. The normal range of precipitation is more in the 20 to 40 inches range for coastal northern California, unless you are getting particular increased rainfall from mountain uplift rain effect as Kentfield or Ben Lomond do. There are quite a few Western Cape species that are well adapted to seasonally wet/saturated winter soils that later dry out in summer, so winter wet soils are not the problem. The majority of these plants will not take hard frost in combination with winter wet, as they are lower elevation or coastal in habitat. The higher elevation plants from the Drakensberg Mountains are dry in winter and wet in summer, so you will also have to be more careful of providing good winter drainage for anything from there, although most plants from this summer rainfall/high elevation mountains will be more winter cold adapted.

If you're looking to increase water retention of gritty mix, you could increase the amount of any of the following in the mix: Turface Bark Pumice Lava rock Gritty sand (careful, depends on type/amount) Of course, you could also add a bit of soil (very small amounts are okay) or peat (has many caveats). Both of these should be added in limited amounts or else the obvious advantage of gritty mix will be lost. Seems like your two goals are a bit conflicting of each other - holding more water but not holding too much water? For tropical cacti, I am using a completely different (well draining) mix altogether - gritty mix is not an ideal substrate for them. Never grown nerve plants before, so I can't comment on how picky they are. If the plant is healthy and has good roots, perhaps may have some leeway to experiment.